The niche of benthic foraminifera, critical thresholds and proxies

Ecological studies of benthic foraminifera are carried out to explain patte rns of distribution and the dynamics of communities. They are also used to provide data to establish proxy relationships with selected factors. Accord ing to niche theory. the patterns of distribution of benthic foraminifera a re controlled by those environmental factors that have reached their critic al thresholds. For each species, in variable environments, different factor s may be limiting distributions both temporally and spatially. For a specie s or an assemblage to be useful as a proxy its abundance must show a strong correlation with the chosen factor. Since numerous factors influence each species, it is only in those environments where the majority of factors sho w little variation but one particular factor shows significant variation th at the proxy relationship for that factor can be determined. On theoretical grounds, the reliability of using foraminiferal abundance as a proxy of a selected environmental factor should be restricted to the range close to th e upper and lower thresholds. For oxygen, foraminifera are potential proxie s fur the lower limits but once oxygen levels rise to values of perhaps >1 or 2 mi l(-1), there is no longer a relationship between oxygen levels and abundance. By contrast. the flux of organic matter over a large range shows a sufficiently close relationship with foraminiferal assemblages so that t ransfer functions can be derived for the deep sea. However. the relationshi p at species level is far less clear cut. Much more accurate estimates of p rimary productivity and modern organic flux rates art: required to improve the determination of past flux rates. (C) 2001 Elsevier Science B.V. All ri ghts reserved.